This invention relates to a pneumatic radial tire capable of effectively preventing separations at ends of belts.
In general, a pneumatic radial tire includes belt layers consisting of a plurality of belt plies reinforced by cords arranged radially outwardly of carcass layers reinforced by radially extending cords. When such a tire is subjected to a load, the belt plies are pulled to cause the cords embedded therein to slightly tilt and deform. These displacements of the cords progressively increase as the displaced portions are nearer to longitudinal ends of the cords or nearer to ends of the belt plies in their width directions. Moreover, the wider the belt plies, the larger the displacements of the cords. As a result, large circumferential shearing strains occur between the ends of the cords and the rubber about the ends at both ends of the maximum width belt ply in its width directions, resulting often into separations between the ends of the cords and the rubber.
In order to prevent the separations at both the ends of the maximum width belt ply, therefore, an attempt has been made to restrain the displacements of the cords by changing intersection angles of the cords of the belt plies with equatorial planes of tires, moduli and configurations of the belt plies, configurations of the belt layers and the like in various manners.
With such an attempt, however, the separations could not be securely prevented for large-sized tires, for example, used in trucks, buses and large construction vehicles, although separations of relatively small tires used for example for passenger cars are effectively prevented.